1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to a hermetically sealed coin-type cell. The cell is of either a primary or a secondary chemistry.
2. Prior Art
Implantable electrochemical cells are in widespread use. These cells are hermetically sealed using an insulating glass to separate the terminal pin from the case. Power sources of this type prevent internal components, such as the electrolyte, from coming into contact with body tissue or sensitive electrical components of the associated implantable medical device. These cells are easily manufactured in large sizes. However, as cell size becomes smaller, it becomes increasingly more complicated to perform the required welding and fabrication processes.
Often, coin cells are used in applications that require a very small power source. A top and bottom terminal crimped together with an insulating gasket characterized coin cells. Contact between the electrodes and their current collectors are achieved by using stack pressure, which eliminates the need for welding the electrodes to the terminals. Also, since the number of parts is relatively small in a coin cell, this minimizes the need for many manufacturing operations. The problem with coin cells is, however, that the insulating gasket is typically of a polymeric or plastic material. Plastics are porous and do not constitute a hermetic seal. Also, these seals are unreliable and prone to leaking. As such, coin cells of the prior art are not suitable for implantable applications.